Glass laminated products have contributed to society for almost a century. Beyond the well known, every day automotive safety glass used in windshields, glass laminates are used in most forms of the transportation industry. They are utilized as windows for trains, airplanes, ships, and nearly every other mode of transportation. Safety glass is characterized by high impact and penetration resistance and does not scatter glass shards and debris when shattered. Glass laminates find widespread use in architectural applications, as well.
Safety glass typically consists of a sandwich of two glass sheets or panels bonded together with an interlayer of a polymeric film or sheet which is placed between the two glass sheets. One or both of the glass sheets may be replaced with optically clear rigid polymeric sheets such as, for example, sheets of polycarbonate materials. Safety glass has further evolved to include multiple layers of glass and/or polymeric sheets bonded together with interlayers of polymeric films or sheets.
The interlayer is typically made with a relatively thick polymer film or sheet that exhibits toughness and adheres to the glass in the event of a crack or crash. Over the years, a wide variety of polymeric interlayers have been developed to produce laminated products. In general, it is desirable that these polymeric interlayers possess acceptable levels of: optical clarity (haze of less than 4%), impact resistance, penetration resistance, ultraviolet light resistance, long term thermal stability, adhesion to glass and/or other rigid polymeric sheets, ultraviolet light transmittance, moisture absorption, moisture resistance, long term weatherability, among other characteristics. Widely used interlayer materials include complex multi-component compositions comprising polymers such as: polyvinylbutyral (PVB); polyurethane (PU); polyvinylchloride (PVC); metallocene-catalyzed linear low density polyethylenes; ethylenevinyl acetate (EVA); ethylene acid copolymer ionomers; polymeric fatty acid polyamides; polyester resins such as poly(ethylene terephthalate); silicone elastomers; epoxy resins; elastomeric polycarbonates; and the like. Acid copolymers have become more widespread in their use for fabricating transparent laminates.
U.S. Pat. No. 3,344,014 discloses laminated glass products with an ethylene copolymer ionomer interlayer. U.S. Pat. No. 3,404,134 discloses a process of ionically crosslinking certain copolymers which contain carboxylic acids. U.S. Pat. No. 4,663,228 and U.S. Pat. No. 4,668,574 each discloses a transparent laminated article which includes a water insoluble ionomer resin film comprising the metal salt of an ionomer resin prepared from ethylene and methacrylic acid monomers. U.S. Pat. No. 5,344,513 discloses a method for manufacturing a laminated transparent substrate which includes an ethylene copolymer ionomer interlayer. U.S. Pat. No. 5,759,698 discloses laminated glass which includes an interlayer comprising an ionomer resin of ethylene-methacrylic acid copolymer with a metal ion which has been thermoset with an organic peroxide and a silane coupling agent. U.S. Pat. No. 5,763,062 discloses a transparent article comprising an extruded ionomer resin film or sheet having a carboxylic acid content of between about 17 and 40 weight percent, said ionomer resin being essentially free of amines. U.S. Pat. No. 5,895,721 and U.S. Pat. No. 6,238,801 each discloses a glazing which includes a transparent layer of an ionomer resin with improved adhesion through the use of a metal chelate. U.S. Pat. No. 6,150,028 discloses glass laminates which include ionomer resin interlayers and glass with solar control characteristics. U.S. Pat. No. 6,432,522 discloses optically transparent glazing which include interlayers comprising ethylene methacrylic acid which incorporate 15 to 17 weight percent and was partially neutralized with sodium. U.S. Patent Application No. 2002/0155302 discloses a method for preparing a transparent laminated article which includes an interlayer comprising a copolymer of an olefin with 13 to 21 weight percent of methacrylic or acrylic acid monomers partially neutralized with an alkali cation. U.S. Patent Application No. 2003/0044579 discloses a method for preparing a transparent laminated article which includes an interlayer comprising a copolymer of an olefin with 13 to 22 weight percent of methacrylic or acrylic acid monomers partially neutralized with an alkali cation. WO 99/58334 discloses transparent laminates which comprise a polymer of ethylene and methacrylic acid or acrylic acid containing about 14 to 24 weight percent of the acid and having about 10 to 80 percent of the acid neutralized with a metallic ion. WO 00/64670 discloses transparent laminates which comprise a polymer of ethylene and methacrylic acid or acrylic acid containing about 14 to 24 weight percent of the acid and having about 10 to 80 percent of the acid neutralized with a metallic ion. WO 2004/011755 discloses transparent laminates which comprise a polymer of ethylene and methacrylic acid or acrylic acid containing about 14 to 28 weight percent of the acid and having about 20 to 60 percent of the acid neutralized with a metallic ion.
The evolution of the product markets, however, requires even greater adhesion of the interlayer to the glass or rigid material in a laminate. Conventional teaching suggests that one way to increase adhesion in an acid copolymer interlayer is to increase the acid content of the copolymer resin. There are problems with this approach, however. One problem is that high acid resins having acid content of greater than 20 wt % are not available commercially. Also, it is known that certain copolymer resins that have high acid content can have an increased tendency to self-adhere. This can make manufacture and processing of high acid resins difficult, or at least more costly as measures have to be taken to avoid product losses from self-adhesion. For example, storing high acid resin in a refrigerated container, or alternatively the use of slip agents or antiblock additives, could be desirable.
Another problem with using higher acid resins than are commercially available is that it is well known that as adhesion properties increase, the impact toughness of the laminate can deteriorate. Therefore adhesion has heretofore been controlled to a level where the impact performance is acceptable. That is, a balance between adhesion and impact toughness in the laminate has been struck to obtain a commercially viable product offering. Generally this is accomplished by using adhesion control additives in some interlayer materials, or by increasing the level of neutralization in an acid copolymer. Manipulating the neutralization level in an acid copolymer ionomer can cause other property changes, as well. Demands for increased adhesion, therefore, are not easily addressed in a conventional manner due to the expected decrease in impact toughness of the laminates upon increasing the acid content of the interlayer material and other changes that can result.
Further, it has become more desirable that the toughness of certain conventional polymeric interlayers be improved over that of current commercially available resins. As is easily recognized by one of ordinary skill in the art, modifying the intrinsic properties of a resin used in preparing interlayers for transparent laminates can affect other properties of the resin and interlayers produced therefrom. Recognizing this fact, changing the acid level, the neutralization level, or other intrinsic characteristics is not straightforward.
Even more problematical, however, is the fact that commercially available acid copolymer resins need to be cooled quickly in order to provide laminates with desirable optical clarity, which are therefore useful as transparent laminate articles. The recommended cooling rate for laminates comprising conventional acid copolymer ionoplast resins is at least 5° F. per minute (2.78° C./min) or greater. In other words, by way of illustration, it is recommended that a laminate prepared using conventional conditions and a conventional ionoplast resin as interlayer material be cooled from an autoclave temperature of 275° F. (135° C.) to a temperature of 104° F. (40° C.) in less than about 35 minutes. In a practical sense this is not a trivial process condition to meet, however, because manufacturing processes are typically carried out under less than ideal conditions. This can be a problem because laminates comprising conventional ionoplast interlayers exhibit a tendency towards increased haze as the cooling rate is decreased. Differences in equipment and processing conditions can cause variation in product quality, even when carried out in the same facilities. The sensitivity of the optical clarity of an ionoplast interlayer to the cooling rate can be a problem in the manufacture of transparent laminates.
It can be desirable to have an improved resin composition for the purpose of increasing adhesion to rigid substrates, particularly adhesion to glass. It can be even more desirable to have such a resin provide a laminate with at least the same, or preferably with improved impact resistance and toughness. Further, it can be desirable to prepare such a resin wherein an interlayer sheet produced from the resin has improved toughness relative to conventional interlayers. Moreover, it can be desirable to have all of these properties in a laminate that provides good optical clarity when designed for uses where optical clarity is a requirement.